1. Field of the Invention
The present invention relates generally to methods and apparatus for molding concrete products and more particularly to such methods and apparatus for molding concrete products having compressed surfaces at different levels on one side thereof.
2. Description of the Related Art
Machines for molding concrete products such as bricks, pavers, blocks and the like are known in the art. Examples of such machines are disclosed in U.S. Pat. Nos. 5,395,228 and 5,059,110 for apparatus for forming concrete block, both of which are owned by the assignee of the present application and are hereby incorporated herein for all purposes. Concrete products are formed by such machines using mold boxes that are mounted on the machine.
A typical mold box includes a rectangular mold box frame having a pair of opposed parallel mounting brackets that are used to mount the frame on the molding machine. A pair of opposed parallel end plates are disposed between the mounting brackets and complete the mold box frame. Often a plurality of partition plates divide the mold box into separate cavities with a separate block, brick or paver being formed in each cavity.
After, such a mold box is mounted on the molding machine, a substantially planar steel pallet is urged against the underside of the mold box. A feed drawer extends over the box and drops a load of wet product-mix into the box, substantially filling it. Next, a shoe assembly mounted on the molding machine moves downwardly toward the mold frame box. Each shoe includes a compression surface that fits into one of the cavities and compresses the mix, thereby forming a block, e.g., in each mold cavity. Typically the molding machine vibrates the mold box during compression to compact the mix and enhance the strength of the finished product.
After compression, the pallet and shoes moves downwardly at the same rate thus stripping the product from each mold cavity and leaving it sitting on the pallet for curing.
Some concrete products are multilevel products, such as the header block indicated generally at 10 in FIG. 1, rather than being a hexahedron. For example, header block 10 includes a first surface 12 and a second surface 14.
Header block 10 may be formed using a prior art mold box assembly, like mold box assembly 16 in FIGS. 3 and 4. Mold box assembly 16 includes a mold box frame 18 that includes a pair of opposed substantially parallel mounting brackets 20, 22 and a pair of opposed substantially parallel end plates 24, 26. Mounting brackets 20, 22 and end plates 24, 26 are bolted together as shown to form mold box frame 18.
Partition plates 28, 30, 32, 34 divide the mold into three cavities, namely cavity 36, between partition plates 28, 30; cavity 38, between partition plates 30, 32; and cavity 40 between partition plates 32, 34. As will soon be described, a header block--like header block in FIG. 10--is molded in each cavity.
Associated with each cavity is a core bar assembly, like core bar assembly 42 is associated with cavity 36. The core bar assembly includes a substantially vertical divider plate 44 that has a first horizontal flange 46 welded to one end of the divider plate and a second horizontal flange 47 welded to the other end. The divider plate extends between end plates 24, 26. One end of the divider plate is secured to end plate 26 via bolts through holes, like the holes visible in FIG. 3, on flange 46. Flange 47 includes similar bolt holes for securing the other end of the divider plate to end plate 24. Substantially identical core bar assemblies 48, 50 are secured in a like manner to end plates 24, 26.
When mold box assembly is used to form header blocks, like head blocks 10 in FIG. 1, the assembly is mounted on a molding machine, like those referred to above, via mounting brackets 20, 22 in a known manner. A steel pallet 51 is urged against the underside of mold box frame 18. During block molding, a feed drawer assembly (not shown) associated with the molding machine extends over the top of assembly 16 and drops a predetermined load of mix into cavities 36, 38 and 40. Excess mix is scraped from the top of the mold assembly by a scrape-off plate (not shown) associated with the molding machine. The scrape-off plate has a shape complementary to the upper profile of the mold box assembly as viewed in FIG. 4 and is moved across the assembly from one of end plates 24, 26 to the other thus scraping off excess mix.
The block machine includes a head plate (not shown) having shoes (also not shown) mounted thereon that extend downwardly therefrom above each of the cavities in assembly 16. Each cavity is beneath a high shoe and a low shoe. For example, in cavity 36, the high shoe compresses mix in the cavity on the left side of divider plate 44 between partition plate 28 and divider plate 44. The low shoe compresses mix in the cavity between divider plate 44 and partition plate 30. Each of the cavities has associated therewith a corresponding high and low shoe thus compressing the mix to form three header blocks, like header block 10 in FIG. 1.
As known in the art, the mold box assembly is vibrated during compression to compact the mix. This increases the strength of the compressed product. After sufficient compression and vibration, steel pallet 51 is lowered from the underside of the mold box assembly while the shoes are lowered thus stripping the product from mold box assembly 16 and leaving three blocks, like block 10, sitting on pallet 51.
Mold box assembly 16 is disadvantageous because special baffles, wiper assemblies and a scrape-off plate must be installed on the molding machine to use mold box assembly 16 to make header blocks. This causes the molding machine to be down for substantial periods when changing to or from a header-block making operation using a mold box assembly like assembly 16.
Another prior art mold box assembly and method is used to make a hollow core header block, like header block 52 in FIG. 2. Header block 52 includes a front surface 53 and a pair of hollow cores 54, 56 that are formed by a pair of corresponding core forms 58, 60 on a core bar assembly 62. Header block 52 includes an upper compressed surface 64, a lower compressed surface 66 and a pair of chamfered surfaces 68, 70.
Core bar assembly 62 includes a core bar 72 to which of each core form 58, 60 is attached. Each core form, like core form 58--which depends from core bar 72--includes a lower-surface portion, like lower-surface portion 74 on core form 58. A downwardly directed shoulder 76 defines the transition between lower-surface portion 74 and an upper-surface portion 78. Surface 70 is formed by a corresponding chamfer (not visible) on the underside of shoulder 76. Core form 60 is similarly constructed.
In operation, core bar assembly 62 is suspended from a pair of opposed parallel end plates in a mold box assembly including end plates and mounting brackets. A pair of partition plates extend from one end plate to another to define front and rear surfaces, like front surface 53 and the opposed parallel rear surface (not visible) of header block 52. The lower-most surface of core forms 58, 60 is urged against a steel pallet (not shown) that is urged against the underside of the mold box assembly.
When wet product mix is dropped into the mold box frame, the high side of the header block fills between core forms 58, 60 to a level slightly above upper surface 64. The low side of the cavity in which block 52 is formed, however, fills only to a level slightly above surface 66. This is due to the narrower dimension defined between upper-surface portion 78 and the partition plate relative to the wider dimension between the core form and the rear surface--opposite surface 74--of block 52. Because the low side of block 52 is approximately half the height of the rear side, the surface area of surface 66 is approximately half the surface area of surface 64. It can therefore be seen that only about half of the mix is supplied to the low side of the mold than to the rear side of the mold.
Although the foregoing procedure is adequate to make hollow core header blocks, it can not be used to make solid header blocks, like header block 10 in FIG. 1.
It is accordingly an object of the present invention to provide a method and apparatus for making multilevel blocks, like header blocks, which overcomes the disadvantages associated with prior art methods and apparatus.
It is more specific object to provide such a method and apparatus that utilizes a mold box assembly that can be quickly installed on and removed from a block making machine.
It is another more specific object of the present invention to provide such a method and apparatus that produces a relatively strong block by compressing a substantial portion of the lower level block surface.
It is still another more specific object of the present invention to provide such a method and apparatus that distributes compression relatively uniformly over the lower block surface.
It is yet another more specific object of the present invention to provide such a method and apparatus that may be used to make solid multilevel blocks.